An upright vacuum cleaner typically comprises a main body containing dirt and dust separating apparatus, a cleaner head mounted on the main body and having a suction opening, and a motor-driven fan unit for drawing dirt-bearing air through the suction opening. The dirt-bearing air is conveyed to the separating apparatus so that dirt and dust can be separated from the air before the air is expelled to the atmosphere.
The suction opening is directed downwardly to face the floor surface to be cleaned. The separating apparatus can take the form of a filter, a filter bag or, as is known, a cyclonic arrangement. The present invention is not concerned with the nature of the separating apparatus and is therefore applicable to vacuum cleaners utilizing any of the above arrangements or another suitable separating apparatus.
A driven agitator, usually in the form of a brush bar, is supported in the cleaner head so as to protrude to a small extent from the suction opening. The brush bar is activated mainly when the vacuum cleaner is used to clean carpeted surfaces. The brush bar comprises an elongate cylindrical core bearing bristles which extend radially outward from the core. The brush bar may be driven by an air turbine or by an electric motor powered by a power supply derived from the main body of the cleaner. The brush bar may be driven by the motor via a drive belt, or may be driven directly by the motor, so as to rotate within the suction opening. Rotation of the brush bar causes the bristles to sweep along the surface of the carpet to be cleaned to loosen dirt and dust, and pick up debris. The suction of air causes air to flow underneath the sole plate and around the brush bar to help lift the dirt and dust from the surface of the carpet and then carry it from the suction opening through the cleaner head towards the separating apparatus.
For example, GB 2,388,306 describes a cleaner head having a brush bar chamber housing a rotatable brush bar. A turbine for driving the brush bar is located in a turbine chamber disposed behind a rectangular air outlet from the brush bar chamber so as to be driven by the airflow emitted from the brush bar chamber. The turbine is connected to the brush bar by a timing belt which extends into the brush bar chamber to one side of the air outlet. The timing belt is located within a belt housing which divides the brush bar chamber into a relatively large first section and a relatively small second section each containing part of the brush bar. As the air outlet is located wholly within the first section of the brush bar chamber, a pressure differential can be generated between the two sections of the brush bar chamber during use of the cleaner head, which can compromise the passage of air from the second section of the brush bar chamber to the air outlet and thereby compromise the pick up performance of the cleaner head.